text:
Which air transport aircraft have a lavatory included inside the cockpit?
Another answer on SE Aviation (Why pilots would leave the cockpit in a short flight?
) had this bit of information in it:

The cockpit of some airliners lacks a lavatory.

Isn't is more the other way around: i.e. A Lavatory inside a cockpit is a rarity?
Which airliner cockpits have an entire Lavatory inside them?
I always thought the Flight Crew came out to use the forward-most Business / First class lavatory.

http://www.wilfredasuquo.com/2015/03/just-my-imagination-as-pilot-toilet-in.html?m=1

I suppose it depends on how the airline orders the aircraft. Although with the secured cockpits I wouldn't be surprised if it is becoming more common

As far as I know, some Boeing 747-400s (BA, Air France) had lavatories inside the cockpit. Apparently, Boeing 747-8 Intercontinental has a lavatory behind the cockpit door:

... Lufthansa Boeing 747-8 Intercontinental is unique in that the flight deck crew have their own lavatory, ... behind the locked cockpit door, allowing for extra security and a non-disruptive cabin service involving trolleys blocking the door.


text:
Would it be feasible for a typical passenger jet to carry along its own Oxidizer?
We know that many Space Shuttles / Rockets etc. carry their own oxidizer with them. This is partly because at the heights they operate the atmosphere is too rarefied to have enough oxygen to sustain the combustion rates they need.
But also, the liquid oxidizer means small pumps can be used instead of massive compressor stages. Which motivates the following question:
Would it be feasible for a typical passenger jet to carry along its own Oxidizer? I am looking for a back of the envelope feasibility calculation. It intuitively sounds impractical but I'm just curious to see some back of the envelope estimates of how much ( weight / volume) of Liq. O2 tanks would be needed if we hypothetically had something like a B-747  with its own cryogenic Oxygen tanks in addition to already extant massive fuel tanks.
Partially motivated by this related SE Aviation Question and a comment by User @Freeman:
How do rocket engines produce more thrust than aircraft jet engines?

Don't forget to allocate space and weight for the cooling system since a 747 flight is a lot longer than your average rockets "let's escape earth" run.

@JustSid: Don't bother. You run the engines on the evaporated oxygen. The amount of evaporated oxygen depends only on the tank isolation as the enthalpy of vaporization is constant, as is the temperature of boiling oxygen under constant pressure.

Using cryogenic fluids mean dealing with low temperatures. That's a totally different approach and resulting complexity than air compressors. Safety will need to be dealt differently too (refueling, topping after a long wait, etc). Leaking O2 near hot burners or brakes is not the same than leaking kerosene.

The point in commercial aviation is not to get as much thrust as you can from your powerplant, but to get from A to B reasonably quickly at low enough cost to build in a reasonable profit margin and still offer attractive fares. So, you make the most of what's free and all around you, and don't carry anything you don't have to.

Short answer: Yes for a short-range airliner, but it would cost a couple of seat rows. No for long-range travel.
Longer answer: To burn 1 kg of Kerosene you need 15.6 kg of air or 3.59 kg of O$_2$. Its density as a liquid is 1.14 kg/l, so it will use 2.65 times the volume of fuel. A cryogenic tank with sufficient insulation is required, though. This means it should have as little surface area per volume as possible. You could not put the LOX into the wing tanks, but need something with a spherical shape somewhere in the fuselage.
If a large commercial airliner needs 100 tons of fuel, it would need to add 359 tons of oxygen. This would be already close to its own takeoff mass, so adding the oxygen will make the airplane too heavy. If, however, you are content with a short-range version of the same airliner that consumes just 20 tons of kerosene for its trip, the needed 72 tons of LOX would require a volume of 63 m³ which is equal to a sphere of 5 m diameter. This would fit nicely into the cabin of a wide body airliner and allow for some insulation. For cg reasons the tank would be right after the wing spar carrythrough, so the airliner would have two short cabins, one ahead and one aft of the tank.
Sorry, the 747 hump cannot be used for LOX storage - the cg shift would be too big.
For running regular jet engines you would still need lots of process gas. To carry that along as well is impossible, even for a short hop. Process gas is all the nitrogen and extra oxygen which is compressed, heated and then ducted through the turbines and accelerated on the way out, but does not actively take part in the combustion. Without that mass of gas thrust would be much lower, or the exhaust speed would need to be much higher for the same thrust, turning the engine into a rocket.

Thanks Peter. I'm confused what you mean by process gas? I grok fuel & oxidizer. Is process gas something different? The only other substance I can see is the various combustion products & any excess air that is pushed through either through the combuster or the bypass.

@curious_cat: Edited with an explanation.

Another nitpickey point: Why do you insist on spherical shaped tanks? Agreed that they do minimize the surface area for a given volume but in routine land transport I see cryogenic trucks carrying Helium / Nitrogen / Air etc. that are just the regular tank truck shape.

If your airliner, A737 or A320 for instance, carries 40,000# of fuel, 144,000# for 72 tons of lox is right in the ballpark of your takeoff gross weight, aircraft + fuel + pax, everything. Still not easy to do! Space required, yes... Weight required, not so much.

On process gas: It's also used to cool the engine. In addition, bleed air from the compressor section is used for things like AC, cabin pressurization, and other things.

@curious_cat Those tankers don't mind a ton more for the tanks. That is different in an aircraft - every excess in tank wall and insulation means fewer paying passengers. I see your point, but tend to respectfully disagree.

@Steve; You're right, but if you carry 72 tons of LOX, you don't need any stinking' process gas for cooling. OK, some for film cooling in the turbine, but much less than normal, because now you can pre-cool it with the LOX on its way to the combustion chamber. Regarding bleed air: Bleed air is wasteful, why else would the 787 do without it? It's more efficient to drive another generator and power the systems electrically.

@PeterKämpf OTOH I see your point too. :) I mean the larger point as to why the whole idea itself is non-feasable / impractical. I am only playing devils advocate to test the smaller bits hypothetically.

An alternative arrangement to deal with CG issues is to have two spherical tanks at either end of the plane.

One thing to consider is that a cryogenic tank does not have to be very thick as it isn't a pressure vessel in the true sense right? A design pressure of say a few bar ought to do fine?

@curious_cat: Right, but a few bar are needed because some oxygen is always cooking off. The spherical tank would minimize this, too.

If I wanted oxidizer in the wing tanks I'd load N2O4.

You could but why would you want to?  One of the advantages to flying in the atmosphere is to use atmospheric oxygen to feed the engines, instead of needing to lug oxidizer around with you.
Finally adding cryo tanks to an aircraft can open up a can of worms worth of development and containment problems.  Liquid oxygen, if not properly contained is extremely dangerous as seen with the Apollo 13 mission or the recent explosion of a SpaceX Falcon9 rocket in Florida while fueling on the pad.
It's just more trouble than it's worth.

"adding crying tanks to a craft beer open up a can of worms". that is such a confusing, yet entertaining phrase...

Damn you, autocorrect!

It's called ‘autocarrot’ for a reason.

Indeed there have been experiments the other direction, using air-breathing engines to assist rocket launches, albeit none that have proven generally useful so far.

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sort: votes


text:
Does Airbus have a production problem?
Looking up numbers for my answer to the A380 production question, it occurs to me that Airbus is facing a real inability to deliver its latest airframes. The A380 is currently sustaining a build pace of 45 aircraft a year with a backlog of about 150 outstanding orders. The A350, Airbus's direct competitor to the 787, has better orders (781 outstanding), but Airbus has been able to deliver only 5 of those, 4 to Qatar Airways and 1 to AerCap. The A340 ended production in 2011, so the 330 (1370 orders, backlog of 356)  350 and 380  are Airbus's only three widebodies in production right now. The 320 and 321 are backlogged badly, though Boeing has a similar backlog for 737 variants so that seems par for the course in the modern aviation industry dominated by LCCs.
Boeing has had fewer orders for its 747-8 but is keeping pace (92 delivered of 123 ordered, averaging 18 airframes a year) and has an embarrassment of riches in 787 orders (1095 ordered, 295 delivered, on pace for about 115 aircraft a year after ramp-up) and healthy business with the older 777 (backlog of 560, in the ballpark of about 80 deliveries a year since 2010). Its 767 frame, a close competitor to the A330, has slightly fewer orders despite being the older plane, but Boeing seems to be keeping pace (less than 100 backlogged in a total of 1161 orders).
I read these numbers and I come to the conclusion that Airbus is in big trouble in the large and very large jet markets it was planning to dominate just ten years ago; Boeing, by most accounts seems to be out-producing them and thus getting the lion's share of a mostly post-jumbo market. Am I reading this right?

What about the A330? It seems absent from the Airbus side of the count.

Edited. The A330, for its size, doesn't seem to be in great demand (neither is the 767), especially with the slightly-larger and much more efficient A350, 777 and 787 in production.

Fair enough, I was just wondering where it fit on your list. I wonder how the military side of the production lines change the numbers though.

@BSteinhurst I would be surprised if Airbus does more military business than Boeing.

When you look at GDP growth and other indicators you will realize that the market cannot absorb 100 + narrow bodies a month over the long term.

The question calls implicitly for opinions. I'm  voting to close it. It could be edited for  focusing on factual elements.

A backlog of orders does not indicate a manufacturing problem. Quite opposite, it is good for the business as it adds stability. Airbus outpaced Boeing on every aircraft expect the A350/787 last year.
Producing all of the backlog in one year is not a good idea, as investments into the production line would be enormous and after a year, utilization of the line would be horrible. If all A380 were to produced this year, what should they do with the production line next year? A chance of another 150 orders per year coming up is unlikely.
A350 production started last year while 787 started in 2011. The ramp-up of production has already happened for the 787, but not for the A350. According to Wikipedia, by 2018 the production has ramped up to 10 per month, which would outpace the 787 at the current capacity.
https://en.wikipedia.org/wiki/Competition_between_Airbus_and_Boeing
https://en.wikipedia.org/wiki/Airbus_A350_XWB#Entry_into_service
In conclusion, I do not think they have a manufacturing problem. Keeping reasonable backlog is good for the business.

Also remember what happened when Boeing ramped up their 737 line - wrong wiring and other defects, causing accidents in operation. It is better to use a well-educated, stable workforce and to ride out the bumps in the order book.

I think that the original question is missing an important point, which is that the backlog was taking so long to get through that customers were jumping from a380 to 748 and from a350 to 773.  A backlog is fantastic...until you start losing customers.

@JayCarr, I don't think that was due to backlog, but rather due to delays in the project. Once ram-up happens, the delivery time is quite reliable, even if long. It is the uncertainty before that that makes customers switch most.

@JanHudec I think we're just saying the same thing in different ways.  I'm calling it backlog because, technically, they were in production (albeit not full capacity), but yes, delays in production is another way of approaching the exact same issue, so I agree with you.

Also, remember that when an airline orders a plane, they know they won't get it immediately, and some of them rely on not getting the planes delivered next month. Backlog is fine because you know what to expect, as long as you're able to supply enough planes for those that need them quickly.

You are correct that Airbus seems to be behind in the widebody market. However, it's not really a production issue, but an orders issue.
In airliner manufacturing, the goal is not to keep backlog at a minimum, but to balance backlog with production. When a customer orders an aircraft, they will be given an estimate for when that aircraft can be delivered. Deliveries are planned years in advance. Delivering aircraft faster may actually be worse, if the customer is not yet ready to take delivery of the aircraft. It does a manufacturer no good to burn through the backlog and run out of orders. Shutting down a production line and restarting it later is more expensive than switching to a new model.
The A380 is a very large plane with not that many orders, so a slower production rate is expected. Also, as we have discussed here, the A380 hasn't received any new orders for a while. Airbus would prefer to keep the line going at least until they decide whether to offer a new engine or stretched version of the plane. The story is similar with the 747, except that the -8 is the new engine/stretched version.
Andri is correct; A350 just recently entered service, and a low production rate is typical for new aircraft while they work out issues. The 787 has been in production for a few years and has already established a higher production rate. Both are still fairly new and so they both have a large backlog of orders to fill.
The A330 does have some remaining orders, many of which are for the future neo version with new engines. The 777 has more backlogged orders, and also has an updated model in development. The 767 is an older design, and has not had any major updates for a while. Although most customers would prefer a newer model, there are still some orders left to fill, including some for the tanker version.

+1. It's really a two-side story, the airlines know they'll get the aircraft in years maybe, and the calculate with this fact usually

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text:
What is the difference between MCP and METO?
I was reading the Cessna 150H POH earlier today and noticed that the manual mentions something like "Normal cruising is done at 65% to 75% of METO power."
The Cessna 172S POH charts refer to cruising power as "75% MCP."
Given that METO stands for "Maximum Except for Take Off" and MCP stands for "Maximum Cruising Power", are the two terms the same thing or do they have differences?

MCP means Max Continuous Power. It is the same thing as METO which means Max Except Takeoff. (Some engines have a time limited takeoff power setting)


text:
What is the minimum takeoff fuel requirement policy for commercial aircraft?
I am currently working on a fuel burn analysis of a particular route (ATL to DCA). I really want to predict takeoff weight of the flight; however, I realized that it's not easy to get the information. Instead, I may want to gather information about minimum fuel requirement for the flight.
For example, I heard from the pilot of the flight that they should have more fuel (20,000lbs) than the minimum fuel (15,000lbs) before takeoff. Could anyone please let me know where I can get this information such as minimum fuel requirement for A320 from ATL to DCA?

This sounds like a college assignment.  The basic legal requirement is sufficient fuel to go from A to B, missed approach at B, fly to alternate airport C, wherever it is (has to be an airport with weather that assures a landing), then land at C with 30 minutes fuel remaining.  A lot of Capts and/or airline policies will add more than 30 minutes to the min fuel to allow for delays due to holding or worse headwinds than forecast.   How this applies to an A320?  You should contact an airline that runs A320s and ask if their Operations dept can help you out.  You might get lucky.

FAR 91.167 requires 45 minutes of cruise flight after the alternate under IFR, which I believe applies to Part 121 carriers.  Correct?

Thanks all for your comments! So, it seems to me that it's also hard to get the information. Perhaps, no one knows the information except airlines?

Welcome to aviation.SE! To be precise, there's a difference between a policy and a regulation. Each airline may set their own policy based on many variables, but the regulations are the same for everyone. If you're asking about regulations, this question would be a good starting point.

Pondlife, thank you so much for your comment! It's really good for me to know the difference between a policy and a regulation. Before I posted this question, I actually already saw the question that you shared. I might want to know 'block fuel' information of a particular route with a particular aircraft.

14 CFR 121.639 Requires an airliner to have enough fuel to reach the destination, then fly to the (most distant) alternate, then fly after that for 45 minutes. If you want to know exactly how much fuel that is for a particular airplane on a particular route, you have to refer to that airplane's POH and plan the flight. It will also depend on the winds aloft and what airport is chosen as the alternate.

I like the idea to take a look pilot operating handbook; however, I doubt if I could get the handbook from open source data.

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text:
Why does the US not have AIREPs?
After looking into aircraft report data at Aviation Weather Center, I realized that PIREP is usually reported inside of US; on the other hand, AIREP is typically reported outside of US. I was wondering if there is any specific/particular reason why AIREP is not available at US territory?

Apples and oranges. A PIREP is a report of current weather conditions at a specific location. An AIREP is primarily a position report, required of some aircraft that are not under radar control. Whereas the primary purpose of a PIREP is to report unusual weather conditions or things like turbulence and are not mandatory, AIREP's are in many cases mandatory and weather information in Section 3 is optional.

Thanks Juan Jimenez for your answer! Based on your comments, I am guessing that AIREP was reported outside of US because aircraft was not under the radar control? In other words, AIREP is not necessarily reported in US territory because it's usually under radar control inside of US?
Please let me correct if I am wrong. Eventually, I might want to obtain wind information reported by pilots inside of US.

AIREPS are not used in the US because all aircraft can be under radar control if need be. But if you are traveling from Florida to Puerto Rico, a US territory, you may not always be in positive radar contact, so you may use them, because you may have to prove you did not make any intervening stops for customs and immigration purposes.


text:
Can I log PIC instrument time in a sim without a current medical or flight review?
Just wondering if one is on land and in a simulator, if you need a current medical and flight review to train and log PIC time?

You can log training time in a simulator but you can't log PIC time.
The rules on logging are in 14 CFR 61.51. There's no requirement anywhere that I can see to have a medical and/or flight review in order to log time.
Logging training time in a simulator is allowed by 61.51(h):

(h) Logging training time. (1) A person may log training time when
  that person receives training from an authorized instructor in an
  aircraft, full flight simulator, flight training device, or aviation
  training device.

But, you cannot log PIC time in a simulator. 61.51(e) says (emphasis mine):

(e) Logging pilot-in-command flight time. (1) A sport,
  recreational, private, commercial, or airline transport pilot may log
  pilot in command flight time for flights-

That means, the only way to log PIC time is in an aircraft.

You can fly a sim without a medical.  Nor do you need a BFR either.  61.58 only applies to operation of an aircraft.  Sims do not count.


text:
What is the relationship between drag and sink rate?
I was just brushing up on basic aerodynamics and I have something I want to clarify about flying in the region of reverse command. I went up in my 172 the other day and noticed the following while practicing slow flight:

I'm on straight and level flight, and I enter slow flight (dirty) the way I usually do. I pull the power back and then I raise the nose to a level attitude slightly to bleed off some airspeed while maintaining the same altitude. When I entered the back side of the power curve, I pitched for an airspeed that was significantly above Vso, but below L/D max, which in this case happened to be 55-56 Knots. However, this time I didn't add any power and I just pitched for 55 knots to see what would happen. The airplane started descending (sinking), which is really what I expected it to do.

My limited understanding of why this happens is that total drag (mostly induced drag at high AOA) exceeds thrust available and the airplane develops a sink to try to regain equilibrium. Is this correct? Can someone with more knowledge explain why this happens? Maybe I'm overthinking it... I just know that high drag at low airspeeds typically results in a high sink rate. I just can't explain exactly why. Some people have said that weight exceeds lift, but I'm pretty sure this isn't the case as the airplane is not stalled.

at higher sink plane is just using more potential energy (altitude) to maintain speed.

Please elaborate on the "this" in "My limited understanding of why this happens is that . . . . "

total drag (mostly induced drag at high AOA) exceeds thrust available and the airplane develops a sink to try to regain equilibrium.

That is exactly right. At best L/D, induced drag is half of total drag and at lower speeds it becomes dominant, growing with the inverse of airspeed squared.

Some people have said that weight exceeds lift, but I'm pretty sure this isn't the case.

You did well not to listen to those people. If the aircraft doesn't accelerate downwards, lift still equals weight. At a constant sink rate the aircraft does not accelerate.
As you say, the aircraft is in an equilibrium. Because you choose to add less power than what was necessary for level flight, the aircraft behaved similar to a glider. Allow me to use a glider for my explanation. Below is one with the dominant forces added as arrows in level flight. Clearly, there is nothing to compensate drag (red):

This airplane is not in equilibrium and does what you did in order to slow down: It flies level while drag is exceeding thrust (which is per definition zero in a glider).
So what to do? Just like when flying a turn, the pilot will now tilt the lift vector. That is the biggest force at his command, and he does so by pitching down. Now the airplane is in a glide, the direction of flight is slightly down and the lift vector (which is per definition perpendicular to the direction of the airspeed, which again is equal to the direction of flight if there is no wind) is equally tilted forward. This is what the next sketch shows:

Now we have a component of lift pointing forward, and that component is equal and opposite to drag. The rest of the lift is needed to compensate the weight, so the lift force is a tiny amount larger than weight. The sink rate is speed times the tilt angle, which in turn is what is needed to have the sine of lift $L$ equal drag $D$. Mathematically speaking, this is:
$$D = L\cdot sin(\gamma)\;\;\;\text{and}\;\;\;\gamma = arcsin\left(\frac{D}{L}\right)$$
with $\gamma$ as the angle of the direction of flight relative to the horizon.
The sink rate $v_z$ is $$v_z = v\cdot sin(\gamma) = v\cdot\frac{D}{L}$$
That is the direct answer to your question: The sink rate is the product of speed and the inverse of the lift-to-drag ratio. At small angles the ratio is approximately equal to its sine when expressed in radians, so I left the trigonometry out of the last equation.

First let's add another point so we can compare all 3 at 55 knots "backside of the power curve".

55 knots straight and level
55 knots descending at partial power
55 knots descending no power.

1 is horizontal to the horizon.  2 is at a descending angle to the horizon. 3 is descending more rapidly.  This is sort of what you do when you approach for landing and modulate your throttle.  Remember PITCH CONTROLS AIRSPEED.  When you cut power, the nose will drop and speed will increase ("the plane develops a sink to try to regain equilibrium"), until the elevator raises the nose, lowering airspeed.
This relationship (equilibrium) of forward set CG and elevator pitch is fundamental in understanding how pitch controls speed.  Now let's add number 4, more power than 1.  Your plane will CLIMB at 55 knots!
Now "high drag at low airspeed typically results in a high sink rate". This is what flaps are for.
The more drag, the steeper the angle of descent.
Notice you can change your angle of descent (sink rate) at CONSTANT AIRSPEED by either reducing power or adding flaps.  Both techniques can be used for landings.


text:
Why does the turn coordinator ball move to the right during a climb?
In a light aircraft like a C172 or PA-28, during a climb the ball in the turn coordinator moves to the right. Why?

What is a "stright" climb?

Not accelerated climb

Does it, though? In a straight and steady climb, the pilot will use rudder input to keep the ball centered. If the pilot does that during the climb, then the ball will only move as the pilot begins and ends the climb.

Well i know that it goes to right but i dont know why .

Welcome to aviation.SE! Are you asking about a typical light, single-engine trainer like the C172? And if you're new to the site, the [tour] may be useful.

Tanks @Pondlife Yes  exaclty in c172 and piper28

OK, thanks for the extra information. I updated your question to make it more specific but if I got it wrong, please just edit it again.

Thanks @pondlife its ok

As a 850+ hour pilot of small planes, I'm with Tanner Swett - not enough rudder.

There are 4 left turning tendencies in aircraft with "clockwise" (as seen from the pilots seat)
turning propeller, 3 of which may apply during a full power climb out.  The four are:

Prop torque  - prop turns right, plane rolls left - more noticeable at high power/slower
  speed
Gyroscopic precession - nose goes down - plane yaws left - not a factor in a climb - some
  effect as plane levels out, also there on tail draggers as rear of plane rises during take off
  roll
Asymmetric prop blade thrust at higher AOA (p factor).  Differences in thrust of ascending
 and descending prop blades will cause yaw to the left.
Spiral slipstream striking vertical stabilizer and side of fuselage, causing yaw to left.

Number 1 has to be watched in higher performance engines during takeoff roll.  Lifting off with insufficient airspeed will cause the plane to roll over and crash.  Fortunately, in a Cessna 172, this tendency is much more modest but should not be ignored.
3 and 4 are probably the main culprits of left yawing tendency in the climb.  The answer:  pitch to safe climbing airspeed (generally Vy) at full power and "step on that ball" with
right rudder.
Post script:  the rolling tendency caused by high power lower speed torque may cause the pilot to feed in more right aileron when the better input is coordinated with rudder.  As the plane accelerates from rotation and liftoff speed to Vy, it would be easy to miss you've rolled slightly to the right due to increased aerodynamic force.  In straight line flight this would not be a major problem (unless you were dangerously near aileron reversal stall speed).  I would work on glancing down at the ball as soon as safe climb is established, perhaps while checking airspeed.  Stay coordinated.

If the ball is offset it means the airplane is accelerating laterally, that is, it's slewing to the side as it flies.  Torque from the engine, plus the spiral flow from the propeller wake and asymmetric thrust from the propeller disc, is doing it and the higher the power setting/the lower the speed, the worse it is.
Vertical fins typically have a bit of directional offset to correct for this in the cruise case without having to add rudder (look carefully at the dorsal fin on a 172, and you'll see it isn't aligned perfectly down the centerline but points to the left a couple degrees), but at high power settings and low speeds, like in a climb, the fin offset isn't enough and some right rudder input is also required to center the ball.
It's the same reason you need a lot of right rudder on takeoff.  If the engine rotated the other way, everything would be opposite and you'd need left rudder.  Engines themselves are also offset in the mount, canted to the right a little bit, for the same purpose.
If you are sufficiently sensitive to it you will feel the side slip in your body, which will want to slouch in the same direction as the skid ball (because that's where the apparent gravity is) and you can maintain reasonably coordinated flight without looking at the ball.


text:
Which aircraft is depicted on 1941 U.S. Post Office airmail stamps?
Between June 25, 1941 and October 29, 1941 a tri-tailed “Twin Motored Transport Plane” was featured on U.S. airmail stamps in 6-, 8-, 10-, 15-, 20- and 50-cent dominations.

Source
Was the aircraft featured on those stamps an actual aircraft, or was it a Postal Service graphic artist’s conceptualization of one?

It appears to be only an artist's conception and is an amalgam of several different designs, but apparently largely based on the Douglas DC-3 aircraft, the Lockheed Electra, and the Beech 18.

The livery bears a striking resemblance to American Airline's DC-3 sleeper service, which operated during that era.

http://usstampgallery.com/view.php?id=1021c6191539bc1ca404bccf78595b7fdc0f06fd

The tail is also reminiscent of the DC-4E

Excellent comment.  The fuselage section above the engine has definitely been taken from the DC-4E -- in particular note the small rectangular windows just above each of the main cabin's windows.

YouTube has several very good taxiing, in-flight, and information videos of/on Douglas' experimental DC-4E and the subsequent sale of that prototype to Japan where it was used as a prototype for a Japanese WWII  4-engine bomber.

authors: К. Келлогг Смиф


text:
What are these strange clouds on the wing and how do they form?
I am having a little trouble figuring out what these strange clouds are. You have a cloud forming off of a fighter jet when it breaks the sound barrier, but this is a different situation.

@mins Ah, yes.  Thanks, A wee typo.  I'll edit.  Shall we delete the other comments to clean up?

but this is a different situation. no it's not. Both condensation caused by decompression

@Federico: Ethan doesn't say that (the link to the duplicate was added after he wrote)

Duplicate questions shouldn't be downvoted just for being duplicates. Being a duplicate doesn't make it a bad question, just a redundant one.

Ethan, what makes you think that breaking the sound "barrier" produces clouds? Condensation cones happen only in subsonic flight.


text:
How much does it cost to build a Boeing 737 NG?
I don't mean how much is the list price. I am asking how much does it cost for Boeing to buy the engine, wing, etc. and put it together and ship it. What is the total cost of ordering everything and putting it together?

Buy the engine, wing etc??? What about the RnD for all these? It's not that simple as "purchasing" the items. Someone needs to develop them and sometimes they are developed for the specific project. And what about parts transportation?

@SteliosAdamantidis This is what I meant by etc. meaning other parts.

It is a reasonable economic question to assess the cost of production of the next plane. The jargon would be the marginal cost of production.

It is hard to determine the cost, regardless the price change of raw material, other cost may vary when time past.

Using different accounting standard like GAAP or IFRS may show different cost; as well as adopting different accounting principle.

This is asking for guesses & opinions.  Nobody who has anything close to authentic figures for what it costs Boeing is going to be posting anything that even looks or sounds like a number on a site like this.  Even setting aside the myriad of ways that you account for the costs that are "per assembly line" rather than "per airframe," real numbers like this are highly sensitive & Boeing keeps data like this highly confidential.

This question is quite hard to answer. Many commercial data are confidential. You may estimate separately R&D (spent once), raw materials (variyng in time, even between purchase by Boeing, beginning of assembly, end of aircraft's assembly, livery to cosutmer and payment), building or retrofit cost.

Ralph is correct. Also, the marginal cost of building one 737 would be quite misleading, since a lot of the cost of building almost any aircraft comes from the one-time R&D and certification costs. Those are well into the billions of dollars for a new airliner these days. Even the R&D and certification costs of updating an existing family of airliners is often well in the billions today.


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Why can't there be more than 4 anti-shock bodies on each wing?
Most airliners have 3 or 4 shock bodies to reduce wave drag. But why can't there be more anti-shock bodies per wing?

why can't who said that?

Which aircraft do you think would benefit from more ASB than it already have, and why?

This is a perfectly good question, with a perfectly good answer. Question: Is there a reason why aircraft seem to be limited to a certain number of anti-shock bodies that can be placed on a wing? Answer: Not in principle, but constraints keep the number down. There was no reason to vote the question down.

@DanieleProcida the question in your comment is not the question being asked. "why can't" assumes that an impossibility exists and is well known, your version doesn't. And at the time OP asked several questions always starting with "why can't", prompting users to edit their posts first, explain them why it was not a good way to ask later, and downvote at the end.

There is no reason to limit the number of anti-shock bodies to 3 or 4. In most modern aircraft, the anti-shock bodies are the flap track fairings which usually house the flap mechanisms.
As such, their number is determined by among other things, the wingspan, the size of control surfaces and the number of actuators required for their actuation etc. This usually limits their number to around 4 due to weight and other considerations.
However, there is no reason there should only be 3 or 4 of them. For example, the Antonov An-225 Mriya has a whole lot of them.

Source:www.avioners.net

There can be, as aeroalias already demonstrated.
However, it would not be better.
Transsonic flow behaves strangely. It cares more about the total cross-section than its distribution. So for the wave-drag reduction it does not matter much whether there are two larger or many smaller anti-shock bodies.
However more anti-shock bodies with the same total cross-section have more surface area and higher surface area causes more friction drag. So more anti-shock is not advantageous.


text:
How much thrust do you lose by putting chevrons on a engine?
The chevrons on a 787 are there exactly to decrease a type of drag that makes the engine louder, but the chevrons form vortices causing more drag. How much thrust is lost from the vortices on the chevrons?

Can somebody please edit the question and add a picture of a 787 chevrons on the engine. Sorry I'm using my laptop this morning and it can't upload images.

When you are unable to upload image, you can put links to images taken from well known websites (airliners.net, wikimedia,...).

also the imgur interface to upload images in not machine-dependant, afaik.

SImilar Questions: http://aviation.stackexchange.com/q/16500/1289. http://aviation.stackexchange.com/q/12832/1289 This Q is different mainly in that it asks (implicitly) for numbers.

The main purpose of the Chevrons is the reduction of engine noise. During research into this, NASA tested a number of configurations under simulated flying conditions and measured the nozzle thrust coefficient given by,
$C_{T_{r}} = \frac{F^{d}_{g}}{F^{i}_{g}}$
where,
$F^{d}_{g}$ is the measure gross thrust and
$F^{i}_{g}$ is the ideal gross thrust
We have,
$F^{i}_{g}$ = .{m}$_{c} v_{i,c}$ + .{m}$_{f} v_{i,f}$
where .{m}$_{c}$ is mass flow rate of core, .{m}$_{f}$ is mass flow rate of fan and $v_{i,c}$ and $v_{i,f}$ are core and fan ideally expanded jet velocities respectively.
The reduction in nozzle thrust coefficient was compared with baseline (no modifications) configuration.

Source: NASA/TM—2000-209948
The configuration used in engine (Chevrons in the fan and nothing in the nozzle produced the lowest loss of thrust coefficient, 0.18.
However, the noise reduction was lesser in this configuration compared to the others. Further modifications have been carried out in the chevrons used in production engines (they are rounded, for one). So, the noise reduction has been obviously improved, though the minimal loss of thrust would've been maintained.
Note: All data from Acoustics and Thrust of Separate-Flow Exhaust Nozzles With Mixing Devices for High-Bypass-Ratio Engines, Naseem H. Saiyed, Kevin L. Mikkelsen and James E. Bridges, Prepared for Prepared for the
Sixth Aeroacoustics Conference and Exhibit, Lahaina, Hawaii, June 12–14, 2000

With $C_T$ defined as actual thrust over ideal thrust, wouldn't $C_T = 0.18$ mean you're only getting 18% of the ideal thrust?  Or do you mean that $C_T$ decreased by 0.18?  That's still huge, isn't it?  If the starting value was perfect efficiency ($C_T = 1.0$), losing 0.18 would take you down to 82% efficiency.  i.e. you've lost nearly 1/5th of the engine's thrust!  That seems like a lot, and not something you'd call minimal.  (I didn't try to find a copy of the paper.  If you have it, maybe you can clarify what the actual thrust ratio is between original and noise-reduced.)


text:
Why do blimps have fins?
Why do blimps have fins? Can't the two (or so) engines already control direction?

What if the engines fail? In early airships this happened frequently, and many ships limped home on a reduced number of engines.
Note that all airships were both vertically and laterally unstable. The helmsman had to continuously adjust the rudder angle to keep the ship on course. In NACA TN 204, Frank Rizzo concluded that enlarging the fins would be beneficial, and reducing them would be unwise. They were just as large as needed to control the ship, but not sufficiently large to give it static stability.
Static stability in aircraft means any attitude change creates forces which return the craft to its old attitude. In airships, several types of static stability must be observed:

Buoyancy: If the ship rises or sinks, the rate of cooling of the atmosphere and the gas in the hull might differ. If the cooling rate of the atmosphere (lapse rate) is above the adiabatic rate, the ship is unstable.
Pitch attitude: If the ship pitches up or down, the lifting gas will shift towards the highest point, and the heavier gas in the ballonets will shift to the lower point, creating an unstable pitch condition.
Directional stability: When moving forward, any heading change will cause a side force which is centered at the forward hull and pushes the ship further off course. The fins create a counteracting force, but due to their size this force is too small to turn the ship back. Only by adding rudder the helmsman can keep the ship stable.
Longitudinal stability: In a similar way, pitching the ship up or down while in motion will create a destabilizing force on the forward hull which is mitigated, but not eliminated, by the horizontal fins. Elevator deflection is necessary to keep the ship at the desired pitch angle.
Roll stability: Since the center of gravity is below the center of buoyancy, the mass of the gondola will pull an airship right side up. This is also valid when flying turns: Then the gondola will roll the ship into the turn such that a rudder command into the turn will also cause a nose-down pitching moment. Now all control surfaces need to be coordinated to keep the nose of the airship up.

Note that only the first and last type of static stability are ensured, and the first only for special atmospheric conditions! The other three are lacking!
Zeppelin airships used two helmsmen, one for directional and one for pitch control. Due to the size of the ships any movement was very slow, so the task of keeping them on course was easier than it might sound. However, taking any of the fins away or even reducing their size would had made the ships uncontrollable.

You mentioned pitch stability twice but didn't mention roll stability at all.

@ratchetfreak: In roll airships are stable. That's boring.

Does the lapse rate matter to rigid and semi-rigid airships? I thought their envelope does not allow expansion, so both volume and mass should stay almost constant, making the ship always stable in altitude, no?

@JanHudec: The expansion still happens in the single gas cells and pushes air out of the ventilated hull - since pressure cannot be controlled, volume changes with temperature, making all types of airships unstable as soon as the lapse rate is higher than the adiabatic rate.

Do you mean there was no active roll control? I.e. if there lateral load unbalance (e.g all cargo or all fuel on one side), there is no way to put the airship laterally horizontal?

Fins, which are also known as stabilizers, increase the horizontal and vertical stability of the blimp.
Without the fins the blimp would porpoise and sway, especially at low speeds.
For example, if the blimp encounters an updraft, the nose would want to rise up, and the tail down. The horizontal stabilizers resist the pitching moment, the same way as the feathers on an arrow.

The fins that are present in the blimps serve two purposes:

They help in controlling the aircraft, much like the normal fixed wing aircraft- the movement of control surfaces in fins (the vertical fins and horizontal stabilizers) helps in rotation of the airship about cg while the engine (i.e. propellers) are used solely for providing thrust in the forward direction.
They also aid in stability- for example, if the airship pointed into the wind turns in one direction due to a disturbance, the wind on the fins creates an opposing moment about the cg and tends to return the craft to its original position. This is especially important in case of tethered blimps or aerostats, which usually lack engines.

No, the fins on airships are too small to return them into the original direction! -1!

@PeterKämpf - "tends to return", not "will return". Perhaps "tends to return" is a very small bit overstated, but "creates a force that contributes to returning the craft to its original direction" is perhaps a bit wordy. But, of course, you are correct.

@KevinFegan: I tend to possibly agree, some conditions pending. Padding answers with weasel words maybe doesn't sometimes enhance potentially the desired clarity, sort of.


text:
How does the control-board on small drones govern their flight?
I saw this YouTube clip for a light weight drone, under a few ounces, with very impressive maneuverability. They used styrofoam for frame and taped the rotors and battery and the control chip to it. It maintains the balance, controls the four motors, pitch and yaw, lift and thrust, basically pilots the drone.  And can do automatic stall recovery or aerobatics?
It seems like the most complex part of these drones, gyro, accelerometer, balance, aviation and navigation (all packed on a tiny board), is the most easy to make and cheapest part!
Can somebody explain to me how the this small flight command center feeds the controls of rotors? Does it have any sense of right side up, gravity? Can it sense the wind by measuring the drift?

https://www.quora.com/How-does-a-MEMS-gyroscope-work

http://hackaday.com/2012/05/22/the-engineer-guy-explains-how-mems-accelerometer-chips-work/

https://github.com/ArduPilot/ardupilot if you want to read associated source code...

Maneuverability with this kind of drone comes with their small size and high thrust-to-weight ratio. When you scale such a dynamic system, the time scales with the square root of size, so the smaller the drone, the higher its agility.
Can it do automatic stall recovery? No, because it never stalls.
Can it do aerobatics? Only figures which are possible with quadcopters if the right control sequence has been pre-programmed. Regular model airplanes can fly pre-programmed aerobatic figures on the press of a button for at least a quarter of a century now.
Does it sense gravity? Yes, by filtering the signals from the accelerometers through a low-pass filter. The dominant vector of the filtered acceleration points down.
Can it sense the wind? Only sudden wind changes, but not constant wind. If you add an absolute reference like a GPS receiver, then yes.
A gyro is a sensor for rotary movements, so it will only sense rotations. It does this with three tiny oscillating structures, orthogonally mounted to each other. A rotation will cause the resulting Coriolis force to move them, affecting their capacitive characteristics, which can be used to measure the turn rate in all three axes.
Accelerometers are needed to measure acceleration, and they also measure gravity. Here again, you will find three tiny, orthogonal structures which are deflected by an acceleration, much like a horizontal beam bends down in Earth's gravity field. Again, capacitive changes are measured and converted to acceleration values in the three axes.
Modern sensors combine both acceleration and turn rate in so-called six-axis sensors (PDF!). They can be run at several Kilohertz, so they take measurements a couple of thousand times per second. This fast rate is needed for the almost instantaneous reaction of virtual reality glasses; the sensors in drones should be happy with a few hundred measurements per second.
A big problem of such miniaturized sensors is their drift: If you only rely on a gyro, you will never be able to tell if the system is truly at rest. If the system is standing still, you can use a 6-axis sensor and take the direction of gravity to remove this drift. But you will still not be able to avoid drift in the rotation around an axis parallel to the gravity vector, plus in a moving system you cannot measure the true direction of gravity, so another sensor is needed which is not affected by movements: A compass. It measures the magnetic field, again in three axes, and can be combined with the first two in 9-axis sensors.
The latest generation of sensors can include an ASIC to run sensor fusion software, so the output is not only digital, but already corrected for drift and presented as quaternions, which are superior for calculating rotations. Also, they include only the two inertial sensors and can act as a sensor hub, so the compass can be placed freely where it is least affected by soft iron effects (PDF!) and is connected via a databus (I²C or SPI).


text:
Do airlines have to get permission from the FAA if they want to change their livery?
Do airlines have to get permission from the FAA to change their livery? It would be great if someone can throw in some examples where this has happened.

Not if they only operate outside the USA :-)

Yeah, We'd like to change ours to say "If you can read this, you're flying too close", is that alright?

Not the FAA, but the manufacturer.
If the parts are composite, only a small range of colors may be approved, depending on the glass transition temperature of the resin matrix. For gliders, only white is allowed for most of the surface area, and similarly composite parts of airliners must be painted in a light color so they don't heat up too much in sunlight. Curiously, the lower surface has the most restrictions, because here the reflected light from a concrete surface and the restricted ventilation create the highest surface temperatures.
Next, the UV absorption capability, moisture protection characteristics and the chemical stability of the paint when in contact with aviation fuel, hydraulic fluids, de-icing fluids and other solvents is important. Composite gliders must use a special topcoat which is more brittle than the composite structure, so cracks will show up. Airliners may use more flexible paints, but must then undergo regular inspections of their composite parts.
Metal surfaces are less demanding and can be painted in any color. Only the area in front of the windshield should be dark enough to reduce glare and irritating reflections.

I believe this also explains a lot of why airlines now all seem to have similar liveries and colors - due to the composite materials.

Are you sure the undersides are most susceptible to heating? Many airlines have a darker colour underneath than on top (e.g., BA and Delta are both dark blue underneath and white on top).

I don't think it's true that you need the manufacturers permission to re-paint, but rather you can only use a certain set of pre-approved colours/paints.

@GavinCoates: Either you accept a limited number of pre-approved paints and hues, or you talk to the manufacturer to make your special design possible. And guess what - the designers rarely accept the standard paints, but want to have something special.

@DavidRicherby: I have this from an Airbus directive from the Eighties, but could not find a reference on the Web. They measured temperatures in hot places like Arizona or Dubai and that was what they recommended. Dark blue is no problem for metallic structures - this was specifically for composites.

@PeterKämpf Thanks for the extra info. It seems that the bellies of BA's 787s are also painted dark blue -- is that part metal?

@DavidRicherby: Yes, it is 350°F autoclave-cured composite material. Back in the Eighties, Airbus wanted to have a 50°C margin between the highest temperature in operation and the material's temperature limits. Now the engineers are more relaxed, especially since the highest temperatures only occur when the structure is only lightly loaded. In flight, all surfaces have much better cooling ;-).

In general, the aircraft owners can paint the aircraft whichever the way they want. However, changing of aircraft liveries comes under refinishing of decorative coatings has to be done by certified personnel as it is considered major maintenance. The materials used should comply to the applicable safety regulations.

That link actually says refinishing of decrative coaatings is considered "preventive maintenance". (That is because it is listed under letter c of that appendix, rather than letter a. I really wish that the legal community would start using indentation to help visually show nesting when making complex lists like that.) That appears (to my quick reading) to really change nothing for air transit carriers, since that still require perfomance and/or supervision by certified personnel.

A short answer, but: No
They can paint their planes pretty much however they want. I imagine various agencies and their customers would have something to say about it if they did something outrageous, but they can repaint their planes without asking permission or even informing the FAA.


text:
Why would a passenger airliner be missing windows in the fuselage?
On many airplanes (you can take the A330 to make an example), the fuselage is not completely covered by windows. In some cases it is due to the presence of the lateral emergency exit, in some other cases I am not sure about the reason. Usually it's above the wings, so I made my idea but I want to know for sure the real reason!
In the linked video, for example, one windows is missing under the "R" of the "Garuda" logo in the fuselage.

I have seen similar missing windows in B737

Most of them are where there is a divider between sections or there is a lavatory there.
Here are the layouts for the Garuda A330-200 and -300. As you can see the divider between the classes (Between Blue row 11 and green row 21) and the lavatories (Between rows 31 and 32) are located where the missing windows are in the video.
-300:

-200:

Images by Garuda Airlines

Some airline which does not have divider also have missed window; for example, Air Asia X also missed the window between frame 39.1 and 39.2, exactly the location under Garuda Logo.

I think you might've uploaded the same image twice.

Quite often there is an air conditioning riser duct in the fuselage wall where there is a blank window space, due to the capacity requirement for the duct itself which is unable to fit between the windows.


text:
What is this tube connected to a 757 for?
In this photo, there is a 757 at Narita Airport with a tube connected to the belly.

Source: Airliners.net
The tube is in the middle of the plane.
There is a similar question about this tube, but here it seems to be connected to the ground and not to the jet bridge.
Does anybody know something about this tube?

You can see on this schematic an input named "ground supply". You see it enters directly in the mixing and distribution unit.

The 757 fell ill, so they plugged an IV line into it.

What Mike said is correct, but I thought I'd add a little more.
The hose is technically called the "PCA Hose" which stands for Pre-Conditioned Air Hose. The hose supplies pre-conditioned air to the aircraft from a ground based unit, that is typically electrically powered and is usually mounted on to each jetbridge. The air can be cold or hot, depending on the needs of the day. The aircraft has a connection that feeds directly into the aircraft's air distribution mix manifold, which is where recirculating air is mixed with fresh pack air before being sent back to the cabin. The ground port connector port has an exterior door and an internal check valve to prevent pressured air from escaping in flight (the 757 actually has two internal check valves that are in series).
When the pre-conditioned air is connected to the aircraft, a small amount of it is sent directly to the cockpit and is 100% fresh (at least on Boeing aircraft), while the remaining PCA air is sent to the mix manifold where it mixed with recirculated cabin air before being released into the cabin.
The main reason to use pre-conditioned air is that it allows the crew to shut off the APU (and air conditioning packs) at the gate, which reduces fuel burn, emissions, noise and maintenance cost. When fuel costs went up dramatically in the mid '00s, there was a major push at airlines to eliminate APU run times, because it is much cheaper to run a ground based, electric air conditioner than running the mini-jet engine to produce bleed air. At the same time, there was also a push to ensure that aircraft were connected to ground electrical power as well, for the same reason.
There are some downsides of using PCA air. First, the hoses get a ton of debris in them and the hoses themselves breakdown internally. All of this debris gets blown back into the aircraft and clogs up the ducts and gaspers. This drives a lot of extra maintenance cost on the air distribution system, which didn't used to require much maintenance. Screens help some, but don't fully fix the problem. Second, ground crew tend to always use the max flow setting on the ground unit, and this can over pressurize ducts on narrowbody aircraft, leading to their failure (especially when the ducts are clogged).
Third, many crews/airports think that on a "hot day" you still have to run the APU, this is false and actually counter productive the cold ground air blows directly on the mix manifold's temperature sensor, so the airplane thinks the air is too cold and starts adding "trim air" from the APU to heat up the mixed air. So running the APU actually makes the cabin hotter, but then the ground crew thinks "since the aircraft is hot with the ground air and APU, imagine how hot it'd be with just the ground air!" I've seen this a lot more at airports where 85F is considered a hot day, as opposed to airports where 105F is considered hot.
Finally, there is a lot of infrastructure and maintenance that goes into all the ground equipment and at some airports, the ground units are actually diesel powered. So at the end of the day, using PCA air and ground power probably save some money, but it definitely isn't "free."
Edit: As to the reason the PCA hose pictured is coming from the ramp instead of the jetbridge, this has to with the infrastructure setup at each airport. There are many systems that can route the PCA air underground. I assume that most of these systems use a centralized plant loop with chilled water/steam pumped throughout the terminal, then use a heat exchanger at each gate. Take a look at the recent setup at SEA for more information: SEA PCA Centralization Project. This Cavotec brochure has some interesting information and graphics as well: Cavotec Brochure (PDF)

The yellow tube you see in the photo is "in-ground air conditioning". It is more common to see it connected to the bridge.

Is it already conditioned that goes directly into the airplane cabin or is it air to be run through the aircraft's packs for conditioning?

It is conditioned air directly into the cabin. A temperature probe is placed near the cabin entrance in order to regulate the temperature.


text:
Why are the runways on Denver Int'l very separated from the terminals?
As you can see in the airport diagram the runways are very separated from the terminals:

I've  found a similar question about Schiphol runways and one of them is very separated because of the noise. But at Denver Airport there are no towns or cities near the runways so, what could be the reason?
Source

Related, required distance between runways

The runways are not distant from the terminals per se but rather from each other.

FAA has published Advisory Circular 150/5300-13A, Airport Design, which includes recommendations for parallel runway separation for US airports.
It summarises:

Quadruple simultaneous precision instrument approaches are currently
  under study by the FAA. In the interim, the FAA, on a case-by-case
  basis, will consider proposals utilizing separations down to a minimum
  of 5,000 feet (1524 m). Quadruples may require special radar,
  monitoring equipment, etc.
Simultaneous non-radar departures require a parallel runway centerline
  separation of at least 3,500 feet (1067 m), and Simultaneous radar
  departures at least 2,500 feet (762 m).

Back to the case, Denver airport is one of the busiest airports in terms of aircraft movements. It needs 6+ runways to support 550K aircraft movements every year. However, the more runways an airport has, the higher the chance air routes will interfere with each other. More separation between runways (and thus the terminals) can reduced distributions.
In fact the airport masterplan (PDF) shows that the operator is planning to build runways further separated from the terminals.
PS1: Denver is not the only case. Many mega airports have been built or are planned to be built with runways far from the terminal buildings, including Dallas/Fort Worth, Washington Dulles, Houston George Bush, as well as Dubai Al Maktoum Airport, Seoul Incheon airport and Shanghai Pudong airport.
PS2: Even though built in less populated area, Denver airport still have noise issues. More details can be seen here and there.

The 34's don't have the separation to do simultaneous ILS approaches to both of them at once (simultaneous visual approaches, yes), so DEN is currently limited to triple simultaneous ILS's -- to 35L, 35R, and one of the 34's. (Same limit landing south.) Which is still a pretty nice capability. LAX can only do 2 ILS's simultaneously, for instance.

@Him and what happens with airports that have their runways very close to each other, like Gatwick?

@kepler22b You can see #fooot comment. I am not sure VMC but for IMC only one runway can be used, mainly 08R/26L in Gatwick. If Gatwick airport expansion project were approved, 08L/26R would be likely downgraded to taxiway.

authors: Софья Харитонова


text:
Why are the leading edges of the 787's horizontal and vertical stabilizers not painted?
The other day I made a question about the engine painting and why it isn't painted at the front part. The answer was: to facilitate anti-ice system.

Source: fervegeon.com
So perhaps the leading edge of the horizontal and vertical stabilizer have a sort of anti-ice system?
And this is not only on the 787; the 777 also has the leading edges unpainted.

Source
And on the 757 and winglet.

Source: flickr

Yes, it uses a heated edge system designed to melt the boundary layer of ice on leading edge surfaces. The system is designed by GKN.

@JanHudec perhaps there is an option to paint them, with a reduction in icing allowances.

@JanHudec Not all aircraft have heated horizontal or vertical stabilizers (for instance, the Learjets only have the horizontal stabilizer heated (electrically), and the Falcons don't heat either one at all).

@JanHudec As I'm sure you know, many aircraft have no anti-icing systems at all, or have only pitot probe heat. I don't think you meant to include these types in your statement, but I just wanted to make sure that is clear to others.

On this video: https://www.youtube.com/watch?v=Q_NjnaUKcIk (minute 16:23-16:55) a man is putting a tube on the leading edge of the wing and then covers it with a bare metal. Perhaps the same happens on the leading edge of horizontal and vetical stabilizers.

The 787 does not have heated empennage leading edges. The anti-ice is only on some of the wing slats. This 787-9 has the Hybrid Laminar Flow Control system integrated into the tailplane leading edges.

I always assumed a lot of leading edges were left unpainted on all kinds of aircraft because of the paint frequently wearing off in those places. Better to leave it neatly unpainted than to have unsightly chips that have to be frequently touched up.

Looks like I might be on to something but not quite right. "Leading edge erosion" is a problem. One solution appears to be applying erosion resistant films to leading edges. I wouldn't be surprised if the films have to be replaced from time to time, and that application and removal of the films might be best done on bare metal rather than painted metal. 3M's page on leading edge films

Another possibility is that leading edges have to be periodically replaced, and it's cheaper to keep the polished aluminum look rather than have custom colors applied for what is essentially a consumable part. Frankly, I suspect erosion is a likely factor in the answer to your question about engine fairings.

Aircraft stabilizers (both vertical and horizontal) usually have metallic leading edges without paint or anti-erosion paint system. This can be seen in the following figure for Airbus A320 family.

Image from Airbus Structure Training Manual
For aircraft with composite stabilizers, leading edge erosion is arrested by bonding metal to the leading edge, or making the leading edge using metal, as in 787:

The .. leading edge assembly, ..., with an aluminum edge and a fiberglass and paper-honeycomb skin.

In such cases, (as @Todd points out), the leading edge is usually left unpainted in order to prevent paint erosion. This method is used in the leading edge of the main rotor blades of a number of helicopters. In such cases, either the bare metal is left as is or a protective film is used to combat erosion.


text:
Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward?
Could an aerofoil be designed to give reasonably good lift for both flow directions?
I was motivated by this related question on Aviation SE: Can a plane fly backward if its propeller is in reverse?
It seems that in practice most wings are indeed optimized for one direction of travel. And that makes sense in the context of the use case they are designed for.
But hypothetically, had a designer to design a wing profile for an aircraft that wanted to be able to fly both ways could it be done? The means of flow reversal could be varied e.g. reversible pitch propellers etc.
Any examples of such profiles?
Why Would You Want To Do This?
I don't have a good answer here. Maybe just curiosity.
More speculation: It could give a fighter or acrobatic aircraft some special manouveres? The ability to reverse without stalling at the end of a steep climb etc.?
Modified Question:
What about an aerofoil that's primarily optimized for forward flow but still has sufficient lift to not perform abyssmally in reverse? i.e. Not strictly symmetric performance. With good lift to drag ratios in forward flight but somewhat draggy in reverse.  Say, a use case where 99% of the flight time is in forward motion but for the other 1% you don't want absolute crap lift in reverse motion.
Perhaps this flexibility can bring out more creativity in the designs?

This one looks like it's 95% there, so I'd take a leap and say "yes, it can be done". But, why would you want to?

@DevSolar I'll add wacky reasons like wanting to land at real narrow airstrips and then sit in the cockpit at the other end & fly off without having to turn? :) Sorry, sounds wacky I know. No good reasons I can come up with really!

A real-world system would probably be based on a system of movable elements. I.e. rotating might turn a control surface on the back of the wing into a rounded nose on the front side.

Models fly with completely flat wings of foamboard, you just need control surfaces on both sides and some way of locking the leading ones off.

I also stumbled over this question and the accepted answer, which, according to other sources, is "totally wrong": http://xkcd.com/803/ (And I registered here mainly to ask a similar question as yours). A basic explaination is given at http://www.explainxkcd.com/wiki/index.php/803:_Airfoil , but one has to differentiate between the cases of flying "upward down" or "backward", of course....

The sharp trailing edge is what gives the Kutta Condition, so if it were sharp both front and back, that could work, though it would be prone to stall due to the sharp leading edge. Another issue is pitch-wise stability.

Related piece of trivia-- typically, a radio-controlled model airplane will still fly if the prop is put on backwards so that the "sharp edge" is leading and the "rounded edge" is trailing.  So the prop airfoil is still creating some thrust, i.e. lift, in this configuration.  However, the performance will be greatly reduced.  Now, as for the pitch-wise stability of a whole airplane flying "backwards"?  I'd say there had better be a computer helping it all work out ok.

I've also seen a photo of a model airplane where the entire wing assembly, which had dihedral, was rubber-banded on to the fuselage upside-down and backwards, so it had anhedral and so the sharp edge was leading and the rounded edge was trailing.  Reportedly it did still fly.

Could your car’s transmission be designed so that reverse gear ratios were identical to forward ratios?  Yes, of course.  If you wanted to drive backwards as often and as fast as you drive forward it would make sense to do so, but most people prefer to travel in the direction they are looking.

There is no airfoil with good lift in both flow directions, but one with some lift is conceivable. However, the lift-to-drag ratio will be nothing to write home about.
One reasonable candidate would be created if we use the forward half of the venerable NACA 66(2)-415 and copy it again for the last half. Like that:

As you might recognize from the plot, this was done with XFOIL. However, the iteration does not converge. But when real air hits this thing, it will create lift, much like a cambered plate will do. Its inviscid zero angle lift coefficient is already 0.5, however, viscous effects will reduce this lift coefficient.
In a good airfoil, the pointed trailing edge defines the point for flow separation, while the rounded nose leaves it to the flow to find a suitable stagnation point. Here we have a rounded contour on both ends, so the separation point widens to a separation area, and this will creep up on the top side once the flow develops some suction at the top. Hence, lift will be poor and drag will be high.
With a little trick, XFOIL can be convinced that this is a regular airfoil with a really blunt trailing edge. Then this is the result at a Reynolds number of 5 million and Mach 0.3:

However, now the separation at the trailing edge is prescribed and will not as easily move up, so the results might be too positive. It seems that L/D exceeds 70 (which surprises me! The original 66(2)-415 has a lower L/D at the same flow conditions, which is a strong hint that we are misusing XFOIL here). Compare that to a good glider airfoil L/D of over 200 at this Reynolds and Mach number.
Applicability
I cannot think of a good reason to do this. The consequences of flying backwards include:

What was stable previously will become unstable - in all directions! Remember that the neutral point is at the quarter chord, measured in flow direction. If the flow direction is reversed, the distance between neutral point and center of gravity will suddenly be more than half the wing chord - in the wrong direction! The same goes for the vertical, which is now destabilizing.
This includes all control surfaces: They will run into their stops and stay at maximum deflection. A manual control system will become unusable, and even a hydraulic, computer-controlled one will experience extreme loads which overpower conventional actuators. When combined with Gurney flaps or directed blowing on both sides, the control issues should become manageable.
If done with reversing a variable-pitch propeller, most of the propeller will not work anymore, because the blade twist runs now opposite to how it should. You could, however, create enough thrust if you use a VJ-101 style propulsion where the engine gondolas swivel through 180°.

VJ-101 (picture source)

EDIT: @Marius mentioned in a comment below the S-72 X-Wing, an attempt to make a helicopter go faster by stopping the rotor above a certain forward speed. The X-Wing actually used an elliptical airfoil and forced the Kutta condition by directed blowing. This enabled it also to use a rigid wing and to adjust blade lift for cyclic and collective control by blowing. This is indeed the only sensible application of an airfoil that works in both directions.

ANOTHER EDIT: I just found this on Airfoiltools.com: The Sikorsky DBLN-526 double ended rotorcraft airfoil. It was most likely used on the S-72, and its 26% would only work with directed blowing, anyway.

If we wanted to compare this to a standard aerofoil (say something used in large commercial aircraft) what would be the lift to drag ratios of both? i.e. How much worse is this?

@curious_cat: This becomes too speculative. I have done a subsonic calculation - doing this in transsonic speeds will probably give even less credible results. I do not have the tools to analyze this airfoil properly.

Thanks! But you still know enough to be sure that "lift will be poor and drag will be high"? Or is there a chance, perhaps after some optimization, that one might end up with an airfoil with not-so-bad lift-to-drag ratios?

@curious_cat: Yes, absolutely!

I assume it would probably be easier to make a wing with a flexible skin stretched over a mechanically manipulatable skeleton, so that the shape of the wing can be changed to produce a correct aerofoil shape in either of the desired directions rather than creating one which is good for both... but i'm just speculating here..

@curious_cat You could probably overcome some of the disadvantages (e.g. for wing controls maybe a spoiler and split flap on either end of the airfoil, with a control computer that uses whichever set happens to be on the trailing edge while keeping the others locked in place), but the basic aerodynamics of the "wing" would still be unfavorable. It may make more sense to take the thrust you'd need to get this off the ground and just point it downward to get airborne (at which point who needs wings?)

I think this is similar to the airfoil used on a stopped-rotor helicopter, such as the S-72 X-Wing (https://www.helis.com/70s/h_s72.php).  I can't find a reference out of have, but I think they use an elliptical airfoil in order get symmetric aerodynamics from the rotor when it is stopped.  They used circulation control to get sufficient lift from the rotor when it was operating normally.

@Marius: This is indeed the only good application of such an airfoil, and I did not think of it at the time when I wrote the answer. Thank you for mentioning the X-Wing!

Apart from frisbees and boomerangs another use for a foil like this would be as a hydrofoil, leeboard or centreboard on a proa or other vessel that sails in both directions. If you had a small hinged flap about 5-10% chord attached to the lower surfaces a few percent back from the edge on each side and free to pivot so that it trailed when it was the trailing edge you might be able to get a cleaner flow separation.

To the list of "consequences of flying backwards" I would include "can't see where you're going"...

Walter Morrison answered this question in the 30s, and found a practical use for it also.
We know it as a flying saucer, or Frisbee.

I don't think there was any concept of flying in the reverse direction, but the Lockheed F-104 had a symmetrical wing.  It was a biconvex shape with a 3.36% thickness ratio.  It had both leading edge slats and trailing edge flaps.  Low speed performance was still less than ideal, but it worked great at Mach 2+.

Yes it can be done - in fact all airfoils have lift capability outside of the normal stall range. The situation of reverse flow can occur in helicopters that travel too fast so that the inboard bit of the retreating blade has reverse flow.
Outside of the normal operational range, all aerofoils behave more or less like flat plates with a second maximum lift coefficient at 45 degrees, and with a drag coefficient that is huge compared with normal operational.
For instance the NACA 0012:

You can see that the lift coefficient at 180 deg is pretty similar to that at zero deg.

Drag coefficient is higher at 180 deg than at 0 deg. A bit difficult to see due to the scale of the graph, but $C_D$ at around 180 degree is easily 10 - 20 times as high as at around 0 degree.

@ymb1 it's from a report from the NASA server, a NACA or NASA report that I used over 10 years ago for making the flight model for a helicopter simulator. The reports were scanned images I believe, I must still have them somewhere but cannot find them.

One place where a reversible aerofoil is used is on the daggerboard of Proas - boats that can be sailed in either direction. They have fixed windward and leeward sides, rather that forward and aft ends, so the foil is always required to generate lift in the same direction, but the flow is reversed.
Their shape is very like that in Peter Kämpf's answer.

The upper wing of Herrick's 'Vertaplane' had a fully symmetrical airfoil where the leading and trailing edges were interchangeable. Of course, that plane didn't fly backwards, but the upper wing could be turned 180º and worked equally well...
https://airandspace.si.edu/collection-objects/herrick-hv-2a-vertaplane

Either of the wings in the diagram will produce lift in both directions, especially the one on the left. The one on the right is the shape of a boomerang wing, so it definitely works. Tilting them to provide a slight angle of attack would give more lift, and less loss at the tip, especially the one on the left, which is curved on both upper & lower sides, making both sides very efficient and provide lots of lift.

Welcome to Av.SE.

Somewhere on the rcgroups.com website I once saw a post describing where someone took the wing of an rc model airplane and flipped it around so that the trailing edge was in front and attached it to the fuselage with rubber bands.  Flight was possible.

Or for fun, how not to do it (FliteTest): https://www.youtube.com/watch?v=Ika-qrX-vhQ

Could an aerofoil be designed to give reasonably good lift for both flow directions

Supersonic airfoil!
Leading edge on supersonic airfoils has to be just as pointy as the trailing edge in order to have an attached oblique shockwave i.e. to avoid a detached shockwave.
A detached shockwave would imply a subsonic airflow past it but at the expense of a higher drag and heating. This effect is normally used to slow down space vehicles reentry: the detached shockwave in front (or beneath in the case of the space shuttle) of the vehicle creates a lot of drag (and heat which has to be somehow shielded).
For supersonic airplane the pointy leading edge implies instead the formation of an attached oblique shockwave: speed past it is still supersonic but drag doesn't increase as much as in the case of a detached one. A famous pointy leading edge was the one of the Lockheed F-104: on the ground, protective guards were installed in order to avoid injuries at the ground personnel.
With a pointy leading and trailing edge, the lift generated by the airfoil is basically independent on the actual shape and is simply proportional to the angle of incidence and Mach number: a supersonic airfoil would work well in both directions.


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What are the FAA regulations concerning controlled descent of a light payload?
I'm part of a High Altitude Ballooning club. Our main goal for this year is to achieve controlled descent of our payload. We plan to use Magnus force cylinders to go about this. I have found nothing in FAA documentation that specifically mentions something of this sort requiring extra clearance, but am still somewhat worried about putting the payload 100,000 feet up and then dropping it down in a controlled manner without being absolutely certain, as an object falling out of the sky in a directed manner could obviously garner concern if people didn't realize what it was. Does anyone know if there are specific regulations for this sort of thing, and whether there are or not, what should I look into doing? Thanks for the help

What is a Magnus Force Cylinder?  Do you have a link to the one that you are using?

The FAA FAR says the following on the matter,

Sec. 91.15
Dropping objects.
No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

As long as you take precautions not to hit anything you are ok. All things considered you are somewhat at the mercy of the FAA here, if something were to go wrong it would most likely be considered your fault.
After some looking around there are some other things to consider. Since you are using Magnus Force Cylinders to control the decent depending on how you look at it these can be considered a "Parachute" by the FAA definition

Parachute: means a device used or intended to be used to retard the fall of a body or object through the air.

Likewise what you are doing may also be considered a "Parachute Drop"

Parachute Drop: means the descent of an object to the surface from an aircraft in flight when a parachute is used or intended to be used during all or part of that descent.

Another interesting point is that from 100,000 ft you will be busting through the Class A airspace here in the US (and likely class E). For that you may want to read up on parachuting in controlled airspace.
Again similar to the dropping, parachuting must be done with caution

§105.5   General
No person may conduct a parachute operation, and no pilot in command of an aircraft may allow a parachute operation to be conducted from an aircraft, if that operation creates a hazard to air traffic or to persons or property on the surface.

Again a lot of this is open to interpretation, since you have no (presumed) way of controlling the vehicle on the decent I would say it does not fall under what the FAA considers a UAS/UAV. You may want to reach out to the FAA directly about doing something like this from the kinds of altitudes you intend to.

Thanks for the response. Is this to say that a light payload which can in some way control its descent (although without propellers/fuel propulsion) simply counts as a dropped object rather than any form of controlled aircraft? If so, that would be great


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Is the airspeed different between above and under the wings?
I heard that when an airplane is flying, air speed or air pressure is higher under the wings. Is it true?

For more on this, see How do wings generate lift?

Yes air travels slower under the wing and faster over the wing, which creating a high pressure under the wing and a low pressure above the wing then the high pressure pushes up on the bottom part of the wing and that's how airplanes generate lift.

How wings really work.

In case of a subsonic attached flow over the cambered airfoil (or a symmetric one at an angle of attack), the airflow speed is higher over the wing and pressure is lower. It is the other way around on the lower surface.

Source: virtualskies.arc.nasa.gov
Note that this is just the mechanics of the flow over the wing. This is not an explanation of lift.

The diagram is a little misleading because it looks like the lower airflow is deflected upwards by the wing, and the stationary point is higher than the trailing edge. This would produce negative lift.

I thought that horse named "equal transit time" had been beaten into falsehood.

@BillOer Certainly, at least to my knowledge, the "equal transit time" is no longer believed to be true, but I can't see anything about the answer that infers "equal transit time". Even if one considers the blue arrows that start at a the same point in front of the wing as time or velocity vectors, note that the top arrow ends before the bottom arrow.

Once again, this is not an explanation for lift. It would be a gross oversimplification and will confuse things. That is why I added that disclaimer. Also, I'm not inferring anything that even remotely says 'equal transit time'. I'm just saying that the pressure above the wing is lower and higher below.

@Terry, that airflow picture looks much like those I've seen for "equal transit time" explanations. But you're right, nothing aeroalias said implied equal transit time.


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What is the average speed used by modern jet fighters when in dogfight?
I am asking this question pertaining to a game I'm designing.
It is well known that many modern jet fighter aircraft can fly at supersonic velocities however I read that this top speed is hardly ever used in combat situations, owing to things like larger turn radius etc.
Can someone tell me a rough estimate of what is the range of speeds most dogfights take place at for modern world jet aircraft?

As designed or in practise?

Practice ofcourse, say jet fighter engagements in gulf war

Mach 0.7, the speed of highest turn rate. See here for more details.

Modern Air Combat Maneuvering takes place between about 350 to 600 KIAS; There is no specific speed but each aircraft has a specific optimal cornering velocity which gives it the greatest rate of turn in order to maximize its maneuverability.  Pilots will seek to maintain this speed when entering a merge as it can give them the greatest maneuvering advantage in order to turn inside on opponent or for jinking to evade a cannon or a missile shot.  As an example, the Lockheed Martin Block 50/52 F-16C has a cornering velocity of 420 KIAS.
Traditionally air combat has been about energy management.  Fighter pilots have something in common with economists in that they are engaged in the art of managing the flow of currency; in the case of the pilot that currency is energy and not money.  The total energy state of a fighter is:
current energy state = energy in - energy out.
The current energy state is the sum of the kinetic energy, proportional to the square of the velocity of the jet and the potential energy of the jet, which is proportional to its height above the ground.  Energy leaves the system in the form of parasite and induced drag acting over a distance as well as loss of altitude, which is proportional to the flat plate area of the jet, load factor, AoA, etc.  Energy enters the system at a rate proportional to the amount of jet fuel burned; this supply is limited to the fuel onboard which again affects the mass of the jet, the induced drag, etc.
So keeping this in mind, a good fighter pilot will seek a way in which he/she can maneuver through space, gaining the best speed and turning performance for the least amount of energy consumed, in order to land in an advantageous position to employ the weapons against an enemy jet.  These kinds of speeds vary between if the jet is on the offensive or defensive in relation to a threat.
So a pilot maintaining that optimal energy state is in the best position to attack, or defend against an attack, and a pilot in a very low energy state is very vulnerable - "low and slow, you're outta dough" - and could be quickly killed in a multi-jet furball.
The cornering velocity is preferred for this reason if maneuvering is anticipated (a given if the jet is about to enter a merge).
With the advent of terminal homing, beyond visual range missiles allowing pilots to stand off from the fight and shoot a threat before it could get close enough to turn with them, higher speed cruise, along with a capability to maneuver well at those higher speeds has become an advantage.  It allows a pilot to more quickly close with an enemy aircraft into the missile's 'no escape' zone, fire, and then turn and dash from the threat, minimizing their presence in an enemy's 'no escape' zone whereby enemy missiles simple don't have the available energy to catch you.  This was the basis for supercruise - supersonic cruise without the use of afterbruners - on the ATF / F-22 program.  Combined with good frontal stealth to minimize the detection range by enemy fighters, supercruise could give a Raptor jock a major advantage in the BVR areana - near invincibility in BVR engagements against non stealthy fighters, if the published results of the Red Flag and other military exercises are to be believed.

"killed in a multi-jet furball" That's what happens when a giant cat licks up the planes and coughs them out again?

@DavidRicherby That's fighter pilot slang for a many v many dog fight.

Average Velocity versus Energy
Average speed would not be the metric I would use to characterize a fight. As has been mentioned, pilots have a certain amount of energy stored in the aircraft configuration and this is what is important. As a pilot, I exchange velocity for altitude (kinetic for potential energy) in a tactical way, like moving chess pieces across the board. This exchange of velocity with altitude comes at a cost though, and the one who manages it the best will win the fight given similarly performing aircraft. In a fight you will have to turn.
To give an average speed, and engagement in the A7-E will extend anywhere between 120 and 650 knots. Given an equal distribution of speeds that would give an average speed of around 385 knots, or 0.6 of the maximum airframe speed.
In my opinion a better metric would be the energy at the start of the engagement and how that is dissipated by the given maneuvers made. This rate of energy loss is specific to a given airframe and maneuver. The turn in the A7-E you wanted to maintain was, if I remember correctly, around 17 units AoA. That said, the principle metric of a fight would be the rate of energy loss.
Remember though, I might chose to lose energy to force my opponent into a particular performance regime within their own aircraft envelope, and in so doing gain an advantage.
This has to also be placed in the context that, "Who gets sight, wins the fight," which is a broader statement than whoever sees the other first will win. It is about cunning and deceit. There are no rules to the fight, except the rules for energy loss and who wants to survive, who is willing to perish.
I entered a fight at maximum airframe speed and at some point ended up taking my opponent straight into a canopy-to-canopy vertical climb. In this position the one who runs out of airspeed and departs into a nose down attitude will lose. I remember thinking don't flinch here. It was a remarkable experience, because the other pilot did the same thing. All I remember is slowly rolling over his canopy within 50 feet, helpless with near zero airspeed, and looking into his cockpit as he looked at me. I had no control over the airframe, and I assume he didn't either.
Finally, you might be in the best fighter pilot in the world, and in the seat of the best aircraft in the world, but if I can out maneuver you prior to the fight with deception and guile I will kill you. This is air combat.
Play in my Sandbox
An aircraft has a sweet spot within their performance envelope, and wants the fight to be fought there. The other aircraft has its own sweet spot and wants the fight to take place in their sandbox. How I keep you in my sandbox, and stay out of yours, is what is important to survival.
Each aircraft has its best turn rate, and when turning in a fight this is where you would want to stay, minimizing energy lost for angles gained on the enemy. It takes discipline to stay at this turn rate, because although your adversary may be gaining angles on you, and creating anxiety by becoming more threatening, they may be losing an unacceptable amount of energy that can be used to your advantage later.
Velocity and altitude is how it gets parsed out. I can exchange kinetic energy for altitude, reducing my speed, and increasing my turn rate. The adversary is using the same credit/debit system of energy. From a neutral position and similar aircraft, who wins the fight has to do with managing the losses more efficiently then the other pilot.
Each aircraft will approach an engagement differently. For example, the A7-E was not designed to be a fighter, and before being retired shared the skies with high performance fighters like the F-16 and F-14. Our tactic for dog fighting was different than what the fighters did.
Bugging Out and Pitching Back
Consider a simple scenario: two sections of similar aircraft in a head on neutral engagement. Both flights have sight. The A7-E's will be in a combat spread with the wingman around a mile abreast the lead. The lead will attempt to split the section of the opposing aircraft. The desire is to pass them with 0 angles, and at least one of us splitting their formation. The attitude I took in an engagement was, "I will hit you head on." And in that mentality I would pass by frighteningly close  with a closure over 1200 knots.
Near passing the other flight the lead would call, "Bug out, bug out," which was the call to the wingman to unload the aircraft to negative 2 G's and accelerate to the highest speed possible while honoring the fight. As the opposing section begins to turn, the A7-E lead will call, "Pitch back, pitch back," and both section and lead begin pulling up at max turn rate turning into one another. As the airspeed decreases the turn rate increases, exchanging airspeed for altitude converting it as efficiently as possible. Towards the apex of the climb the lead and wingman "crossover,", exchanging sides and engaging the adversary head on once more: one mile abreast. Getting the nose directed back into the fight with as much energy as possible, and unloading the aircraft once more.
If the A7-E flight has been successful they will pass the fighters with 0 degrees in angle, or head on. Any difference from head on means that the fighters have gained in the fight. In this scenario the A7-E is using its complete envelope. From maximum range airspeed, to unloaded and maximum airspeed, to low airspeed regimes with high turn radius.
Cunning and Deceit
I want to emphasize this aspect of the fight, which in my experience was not explicit in our training. We were taught the performance envelope, maneuvers, things one can do at certain points in an engagement, but we were not taught how to fight. Here is a case in point. Any game has to be able to effectively capture this.
One of the missions I did as an A7-E pilot was to run missile profiles directed at the Battle Group. In the brief I would be given a radial, distance, and altitude to begin the profile. It was nice for sight-seeing, but not a lot of fun. On one such mission I had my front radio on my controller's frequency, and started flipping through the digital frequencies on the second. Sure it was a long shot, but I was just riding into the Battle Group. I wanted to have some fun.
I would turn to a frequency and listen for maybe 5-10 seconds and move on. On one frequency I heard the controller calling, "Alpha-Bravo-214, your target is at your 2 o'clock, 40 miles, 25,000." I listened longer and realized this was the flight of 2 F-14's being directed to intercept. After a minute or so I had learned that the lead was using the call sign Raven, while the wingman was Dutch.
I listened to the intercept, and just prior to 8 miles, which is the rough rule of thumb for visual contact, I called out, "Dutch, bogey on your six! Break right, break right!" The call for a "break" was a call for an immediate hard turn. After the call there was a long pause. Then I heard the lead call, "Dutch where are you?" The wingman answered back, "You told me to break right." Then there was the standard radio call for an intruder on the net. I was never intercepted that day.


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How does a pilots license of cluster ballooning differ from other ballooning or unpowered flight?
John Ninomiya discusses his experience with developing this new style of ballooning on his Cluster Ballooning website.
Many of the site's links are now broken, but on there he formerly attested that he was granted a pilots' license by the FAA for this style of flight.
I remember the wording clearly suggesting that this license was different than other flight license. Does anyone know how it did, or could have, differed?

Any other relevant history about cluster ballooning is also appreciated.

The license required for operating a manned free balloon would be a "Lighter-than-air, Balloon" license (as opposed to a "regular" license, which is usually thought of as being for "regular" Airplanes - the kind that take off and land using runways, as opposed to lakes).
Cluster balloons are, for all regulatory purposes, just "balloons" - the only difference is rather than having one monolithic envelope filed with hot air like the balloons most of us are used to seeing they have a bunch of smaller envelopes, usually filled with helium.
An Airman Registry Search shows that there is one "John Ninomiya", with a commercial pilot's license for lighter-than-air balloons, which is consistent with what I'd expect.

A lot of the requirements for a private pilot license in balloons are similar to what you need to do to get a private pilot license in an airplane - for example you still need to learn the same regulatory environment, you'll learn to read the same charts, you'll cover flight planning and weather, etc.
The differences are that you'll be learning balloon systems rather than aircraft systems, and the experience requirements under FAR 61.109 are pretty radically different because of the fact that balloon flying is pretty radically different from flying around in an airplane.
You can peruse Part 61 of the FARs for all the specific details on training requirements for lighter-than-air balloon pilot certificates - Subpart E  (Private Pilots) is probably where you want to look.

Note that it's possible that you can have a cluster balloon that you can legally operate with no license, provided it can qualify as an "ultralight balloon" under Part 103 of the FARs - you can read more about that here). Looking at John's rig, I think it's skimpy enough to qualify under those rules...

Perfect answer!

@voretaq7: Here's an unbroken version of that link.